I think a composite mixture of grease and crumbs, and maybe a little corn meal, makes a pretty good gap-filler, but what you've done looks a heck of a lot better.
I tend to think that your best option may be to cover the gap with a set on backsplash. The existing tile could stay as it is. The backsplash could be a strip of granite to match the countertop, or something a little different as an accent. But I think that's the way I would go. I don't think anything in the gap would either work or look very good.